Why does my MultiPlus-II show Low Battery and Overload alarms together when I switch it on?

Read the two LEDs as one message. On MultiPlus and Quattro units, Low Battery and Overload together mean DC ripple: the voltage on the battery cables is swinging because the battery side cannot supply the pulses of current the inverter draws. Blinking together is a pre-alarm; solid together is a shutdown. The fix is on the DC side, and it is almost always the cabling.

If only the Low Battery LED is on and the battery is full, that is a different fault, covered in why a MultiPlus shows low battery on a full battery.

Why it shows up at switch-on

An inverter has large input capacitors, and they draw a big inrush when the battery is connected or the unit starts. That is why an inverter feed wants a slow fuse. Two things turn that inrush into a ripple alarm:

• A lithium BMS that limits. If the battery's management system goes into a limited state, or has a modest peak discharge rating, it cannot supply the pulses the inverter draws. If the alarms appear in the moment you connect the battery or enable the BMS, and clear once the system settles, look at the battery's peak discharge rating and how its BMS handles inrush. The battery maker's datasheet is the authority here.
• A load waiting on AC-out. If an air conditioner, compressor or microwave is switched on when the inverter starts, the start surge lands on a cold system. Switch AC loads off, start the inverter, then bring loads on one at a time. If Overload alone stays solid with nothing connected, look for a short on the AC output.

The checks, in order

1. Measure voltage at both ends under load. Put a meter on the battery posts and on the MultiPlus DC terminals while it inverts. A real difference between the two is cable, lug or fuse loss, and it is the most common cause.
2. Check the cable against the unit. Our install guide's starting figures for a 12V/3000VA unit are roughly 250 to 300 amps of DC current, 2/0 to 4/0 AWG cable and a 300 to 400 amp fuse close to the battery, with the manual as the final word. See what cable a MultiPlus 12/3000 needs.
3. Torque every lug. Loose DC connections at this current make heat and ripple. Stacked ring terminals on a battery post are a regular offender; a busbar fixes that.
4. Check the battery can supply it. An undersized bank, or a BMS in a limited state, produces exactly this alarm. Shorter cables or a bigger bank are the cures.
5. Read the log. A VE.Bus Smart Dongle shows the alarm by name in VictronConnect, and a SmartShunt shows what the battery was doing at that moment.

Before any warranty claim, have a photo of the DC cabling and fuse, the cable gauge and length, the battery type and capacity, and the firmware version. Most "faulty inverter" returns turn out to be installation issues.

Send us those details and we will go through them with you. Everything ships from our warehouse in Upland, California.